1. Field of the Invention
The present invention relates to sensor devices and methods of manufacture thereof. More particularly, the present invention relates to a sensing device and method of manufacture based on photo-formed silicone membranes that are substantially permeable to gaseous molecules, but substantially impermeable to non-gaseous molecules and ions.
2. Background Information
Microfabricated membranes, based on silicone materials, that are substantially permeable to gaseous molecules, but substantially impermeable to non-gaseous molecules and ions, are known. However, the silicone materials that have been used successfully are not directly photoformable. Therefore, indirect means have been used to achieve photo-patterning at specific locations on a surface.
For example, U.S. Pat. No. 5,200,051 teaches an analyte attenuation layer used in an amperometric sensor that contains a siloxane/non-siloxane copolymer. In one embodiment, a dimethylsiloxane-bisphenol A carbonate copolymer, dissolved in a solvent, is spin-coated onto a wafer and then coated with a gelatin photoresist layer. Such a photoresist layer is then patterned by selective exposure to ultraviolet (UV) radiation though a photomask and developed. Such a process leaves photo-cured resist material protecting the underlying copolymer, while the unexposed photoresist layer and the underlying copolymer are removed with a wet etching agent, e.g., tetramethylammonium hydroxide in methanol.
Such an indirect method can enable the copolymer to be photo-patterned, even though it is not itself a photoactive material. However, while the resulting copolymer membrane exhibits metabolite (e.g., glucose) transport attenuation, and is freely permeable to oxygen, the process of manufacture is complex, which lowers yield and raises the cost of the finished product.
Additionally, U.S. Pat. No. 6,030,827 teaches sensor structures for measuring glucose and the like, with microfabricated apertures in a siloxane/non-siloxane copolymer, in which glucose can only enter a matrix through one or more patterned apertures, whereas oxygen passes directly through the copolymer. U.S. Pat. No. 5,514,253 teaches oxygen and carbon dioxide sensor structures with patterned siloxane/non-siloxane copolymer layers.
Furthermore, U.S. Pat. No. 4,933,048 teaches a reference electrode structure that comprises a silver-silver chloride electrode in contact with a matrix containing chloride ions, and an encapsulating layer that is permeable to water vapor, but impermeable to ions. The encapsulating layer can be formed from polyvinyl chloride, polytetrafluoroethylene and silicone rubber. A distal salt bridge exists in the layer to permit exchange of ions with a fluid in contact with the device.
U.S. Pat. No. 6,737,117 teaches a dielectric protective coating material for semiconductor devices in which the coating comprises a siloxane-based resin having a relatively low dielectric constant. The coating material is based on a hydrosilsesquioxane resin that is cured by exposure to ultraviolet light to provide a passivating or scratch-resistant dielectric coat.
Gelest Inc. of Morrisville, Pa. provides a range of ultraviolet cured acrylate-modified silicone elastomers (e.g., ZIPCONE™ U Series), demonstrated to be suitable for cladding of optical components and as elastomeric shields. In addition, U.S. Pat. No. 6,770,726 teaches photo- and thermally-labile siloxane polymers that undergo transformation to SiO2-rich films by elimination of beta-substituted alkyl groups.
Based on the foregoing, a need exists for sensing devices made by simple and reliable manufacturing processes for gas permeable membranes formed in a single convenient step that are impermeable to ions and metabolites.